Dry hydrants are a type of fire service hydrant for use where there is no source of pressurized water. For example, in rural areas where there is no centralized water service, water for fire fighting is commonly drawn from lakes, ponds, cisterns or the like. Typically, a tanker truck will draw water from a nearby body of water using a flexible hose fitted with a strainer to prevent debris from being drawn into the hose. The tanker will then travel to the site the fire, where a pumper truck draws water from the tanker to fight the fire.
To simplify and speed up the process of pumping water from lakes and ponds or the like, many areas have installed dry hydrant systems. A dry hydrant system usually includes a length of pipe having one end disposed below the water line of a body of water and the other end disposed at or near the shoreline. In these arrangements, a length of polyvinylchloride (PVC) pipe is laid in a trench dug from the shoreline of a body of water to enable one end of the pipe to be disposed at a predetermined fixed depth in the water. The other end of the pipe is connected via a 90.degree. elbow to a vertical standpipe. The standpipe is provided with a coupling which enables a standard fire hose to be connected to the standpipe to draw water through the dry hydrant to a tanker truck.
Typical strainers used with dry hydrants or dry hydrant piping systems consist of a pipe with uniformly sized holes drilled along its length. Such strainers either have holes drilled completely around the circumference of the pipe or only partially. Strainers with holes drilled around the complete circumference are generally positioned vertically in the lake or pond. Strainers with holes only partially around the circumference are placed horizontally in the body of water; furthermore, in such an arrangement, the holes face the bottom of the lake or pond. Both of these strainers usually contain a capped end and a suction end to which the PVC piping system is attached. Thus, when the tanker truck draws water via the coupling and PVC piping system, the water is drawn through the holes of the strainer.
In such an arrangement, the strainer must be properly positioned at the correct depth in the body of water. If placed indiscriminately, the strainer may draw debris, leaves or mud from the bottom of the pond of lake which will clog the strainer and diminish the flow of water to the tanker. For example, after a storm, the bottom area under a horizontal or vertical strainer may often be unsettled and shodden with debris. In such circumstances, or even when a strainer is haphazardously positioned in a lake, the suction created by the tanker pump may draw such debris and possibly clog the strainer, the piping system, or even ruin the pump. Such complications waste valuable time and may prevent the saving of property and lives.
In other circumstances, both the horizontal strainer and the vertical strainer may be too close to the surface of the water. Such instances commonly occur in areas with low tides, dry seasons, or periodic changes in water level, such as lakes, ponds, seas, bays, or rivers. When the water level is low and too close to the strainer, the suction created by the tanker pump often creates whirlpool vortices. Such vortices cause air to enter the strainer, which in turn causes pump cavitation, and ultimately, pump failure. This problem also impairs the ability of fire fighters to save property and lives.
The above described problems generally occur because dry hydrant strainers typically employ a uniform drill pattern and constant hole diameter. The size, location, and number of the holes creates a concentrated zone of low pressure near the suction end of the strainer. Thus, the holes near the suction end of the strainer experience high suction and high water flow rates, while those near the capped end of the strainer experience very little suction and low water flow rates. Because the high suction and high flow rates are concentrated in one area, the low pressure area and zone of accelerating water outside the strainer extend far away from the outer surface of the strainer. This phenomena dramatically increases the likelihood of whirlpool vortices and the drawing of debris. The hole design of these strainers also create uneven backflushing when reversing flow through the strainer in an attempt to remove debris.
The previous described problems associated with current dry hydrant strainers limit their range of use. Sources of available water are often full of debris and may be very shallow. Because of the above identified problems of current strainers, dry hydrants may not be used in some bodies of water. Thus, tanker trucks must travel further distances to receive water from deeper or less debris shodden waters. The previously described constraints of current dry hydrant strainers has created a need for a solution.